Cover for airbag

Abstract: A resilient plastic cover for an air bag of a vehicle occupant restraint system including a front wall (10) with tear lines (20, 22) positioned inwardly from outer margins of the front wall and which define two substantially rectangular doors which rotate open about door hinges when the air bag is deployed. Pairs of arcuate secondary tear lines (26, 28) extend from each first tear line (20, 22) to the outer margins of the cover front wall (20) permitting wide opening of the doors. A thinned region of the cover permits flattening of a hinge axis and thickened cover region adjacent to the secondary tear lines (26, 28) prevents tearing between each pair of secondary tear lines.

Description: This invention relates to airbags for automotive crash protection. More specifically, it relates to an improved cover for an airbag installation. Automotive airbags are commonly installed to protect both the driver and the front seat passenger from injury in the event of a head-on collision. The term "airbag" is something of a misnomer because typically the bag is filled with a rapidly evolving gas produced by an igniter. The bag is designed to inflate in no more than approximately 15 milliseconds. In its uninflated and folded condition it is mounted within a housing having a cover which is designed to tear along predetermined lines to provide an opening for the escape of the airbag. In view of the explosive nature of the airbag inflation, one of the major problems with prior art installations has been the tendency of the airbag cover to break into pieces. The pieces thereupon become projectiles capable of striking the occupants. Airbag covers customarily are formed of materials such as thermoplastics which are somewhat resilient and have weakened or thinned regions forming tear lines. The tear lines are designed to rupture and form one or more hinged doors which permit the expanding airbag to escape. Ideally the shearing stress which bursts the tear lines is dissipated within sufficient time and distance to allow the formation of hinges which permit the doors to open but retain them in place on the cover. One such airbag module cover is disclosed in EP-A-0489922 (on which the pre-characterizing part of claim 1 is based). The cover includes two substantially rectangular doors defined by an "H" shaped tear line pattern which doors have side edges spaced inwardly from those of the cover. The tear line pattern has peripheral portions which extend outwardly to upper and lower edges of a front surface of the cover. Upon deployment of an airbag contained by the cover, the tear lines rupture permitting each door to hinge outwardly about a hinge line located along an upper or lower edge of the front surface of the cover. The extent of hingeing is accordingly limited by the interconnection between each door and a side portion of the cover. It would be desirable for the doors to swing open through an arc exceeding 180° in order for them to be positioned well clear of the expanding airbag. Finally, it would be desirable to achieve these objectives while employing a one piece molded cover without the need for inserts or hardware elements. Thus according to the invention there is provided a vehicle occupant restraint airbag module cover as set out in claim 1. The door hinges so formed will be positioned at one of the front wall margins. One of said front wall margins may be curved prior to rupture and resiliently formed into a substantially straight configuration upon formation of one of said hinges. Preferably the cover includes tear preventing means for preventing tearing between each pair of said secondary arcuate tear lines, said tear preventing means comprising a thickened portion of said cover intermediate each pair of secondary arcuate tear lines. Each such thickened portion may comprise a barrier adjacent the respective secondary arcuate tear lines of each pair. Each door hinge may comprise a thinner region of said cover formed between said first and second pairs of secondary tear lines. The cover is preferably formed from a thermoplastic resin. The invention also covers a vehicle occupant restraint system including a cover as described above. FIG. 1 is a front view of the cover of an unactivated driver's side airbag module in accordance with the present invention; FIG. 2 is a view similar to FIG. 1 illustrating the cover after activation with the airbag release doors open; FIG. 3 is an enlarged cross-section taken substantially along the line 3-3 of FIG. 1 ; FIG. 4 is an enlarged cross-section taken substantially along the line 4-4 of FIG. 2 ; and FIG. 5 is an enlarged cross-section taken substantially along the line 5-5 of FIG. 2 . Illustrated in FIGS. 1 and 3 is a molded thermoplastic airbag cover designed for installation in a steering wheel assembly. It comprises a front wall 10 bounded by rearwardly extending sidewalls including a top sidewall 12 and a left sidewall 14 , as well as right and bottom sidewalls which are not illustrated. Molded mounting structures 16 , 18 are employed for mounting the cover to the airbag assembly. However, they form no part of the invention and will not be further described. The front wall 10 may carry a somewhat rectangular groove 20 which is partially aesthetic and partially tear line, as will be further explained. The groove 20 is bisected by a horizontal tear line 22 . It will be understood that the tear lines are thinned and weakened portions which are designed to rupture when the airbag expands. It will be noted that the groove 20 is displaced inwardly from the outer margin 24 of the front wall 10 . In prior art airbag covers having external appearances similar to that of this invention, the groove 20 is also designed to function as a hinge. Accordingly when the tear lines rupture to form doors, the rotation of the doors is restricted to an arc of 180° by the remaining surface of the front wall 10 . In accordance with the present invention, the arc through which the doors may move is greatly increased by moving the hinge of each door to the outer margin 24 of the front wall 10 . This is accomplished by means of arcuate tear lines 26 formed on the inner surface of the front wall 10 and extending from the thin tear line portion of the groove 20 to the outer margin 24 at the top of the cover as shown in FIG. 1 . Similar tear lines 28 , also on the inside of the cover, extend from the bottom portion of groove 20 to the outer margin 24 at the bottom of the cover. FIGS. 2 , 4 and 5 illustrate the manner in which this invention operates. These figures show the cover after rupture of the tear lines to form an upper door 30 and a lower door 32 . As will be noted, the rupture of the tear line 20 leads into the arcuate tear lines 26 at the top of the cover and into the tear lines 28 at the bottom of the cover. As a result, the hinges for the doors are effectively moved to the outer margin 24 of the cover. As the outer margin 24 at the bottom of the cover is substantially straight, the hinge 33 has a substantially linear axis. However, the outer margin 24 at the top of the cover is curved as shown in FIG. 1 . Accordingly, a hinge in this region would tend to result in stress concentrations. This could cause the hinge to tear along its axis. In order to overcome this difficulty, the cover is molded with a thinned and more resilient portion 34 in the hinge region as illustrated in FIG. 5 . The result is that the hinge region 34 flexes inwardly to flatten out and form a linear hinge axis 36 as the airbag deploys and as illustrated in FIG. 2 . As previously explained, it is important to prevent any portion of the cover from detaching and becoming a projectile within the vehicle. Tearing through the thinned hinge region 34 is prevented, as illustrated in FIG. 5 , by providing a thickened safety corner 38 . A safety corner 38 is provided at each of the four arcuate tear lines 26 , 28 . As illustrated in FIG. 5 , each safety corner is on the inside of the tear line and is positioned so as not to interfere with the flexing of the thinned portion 34 and the subsequent flattening of the hinge. Each of the arcuate tear lines 26 is substantially perpendicular to the hinge and extends past it. In actual embodiments of this invention, the thermoplastic polymer cover material is Santoprene and has a thickness of 2.5-3 mm. The tear lines are .4-.75 mm thick. The hinge region 34 is 2 mm thick and 10 mm wide and extends substantially the full length of the door. The safety corners are 3-4 mm thick and 3-10 mm wide. As a result of the present invention, the doors of an activated airbag cover are able to rotate 90° further than prior art covers. This added rotation causes the doors to travel away from the vehicle occupants. Furthermore, hinge formation takes place later in the deployment procedure than is true of prior art devices. Accordingly extra margins of safety are provided which prevent cover parts from hitting vehicle occupants. It is believed that the many advantages of this invention will now be apparent to those skilled in the art. It will also be apparent that a number of variations and modifications may be made therein without departing from its spirit and scope. Accordingly, the foregoing description is to be construed as illustrative only, rather than limiting. This invention is limited only by the scope of the following claims.

Claims: A resilient cover for use in an air bag vehicle occupant restraint system having a front wall (10) defining first tear lines (20, 22) rupturable upon expansion of said air bag to form first and second substantially rectangular hinged doors (30, 32) through which said bag expands, each of said doors (30, 32) having edges displaced inwardly from two opposed sides of said front wall (10), and rearwardly extending sidewalls (12, 14) surrounding said front wall (10) to enclose the unexpanded bag, wherein first and second pairs of secondary arcuate tear lines (26, 28) extend from the first tear lines (20) to outer margin (24) of said front wall (10) thereby forming door hinges (33, 34), characterised in that the doors (30, 32) are surrounded by a groove (20) part of which constitutes said first tear lines and remaining parts of which each extend between one said pair of secondary arcuate tear lines (26, 28) and are spaced inwardly from said outer margin (24) of said front wall (10) whereby upon air bag deployment full swinging motion of the doors (30, 32) is possible. The cover of claim 1 wherein one of said front wall margins (24) is curved prior to rupture and is resiliently forced into a substantially straight configuration upon formation of one of said hinges (34). The cover of claim 1 or 2 wherein said cover includes means (38) for preventing tearing between each pair of said secondary arcuate tear lines (26, 28). The cover of any preceding claim wherein said cover includes tear preventing means (38) for preventing tearing between each pair of said secondary arcuate tear lines (26, 28), said tear preventing means (38) comprises a thickened portion of said cover intermediate each pair of secondary arcuate tear lines (26, 28). The cover of claim 4 wherein said thickened portion (38) comprises a barrier adjacent the respective secondary arcuate tear lines of each pair (26, 28). The cover of claim 2 wherein said door hinge (34) is in a thinner region of said cover. The cover of claim 6 wherein said thinner region of said door hinge is formed between said first and second pairs of secondary tear lines (26, 28). The cover of any preceding claim wherein said cover is formed from a thermoplastic resin. A vehicle occupant restraint system including a cover as claimed in any preceding claim.

Inventors: HARRIS BRADLEY D, LEONELLI F PAUL, HARRIS, BRADLEY D., LEONELLI, F. PAUL
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC. (AN INDIANA CORP.)
Application year: 1994
Main classification: B60R21
IPC codes: B60R21